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On Earth, the Rayleigh number for convection within Earth's mantle is estimated to be of order 10 7, which indicates vigorous convection. This value corresponds to whole mantle convection (i.e. convection extending from the Earth's surface to the border with the core). On a global scale, surface expression of this convection is the tectonic ...
The mantle within about 200 km (120 mi) above the core–mantle boundary appears to have distinctly different seismic properties than the mantle at slightly shallower depths; this unusual mantle region just above the core is called D″ ("D double-prime"), a nomenclature introduced over 50 years ago by the geophysicist Keith Bullen. [26]
Mantle convection is the result of a thermal gradient: the lower mantle is hotter than the upper mantle, and is therefore less dense. This sets up two primary types of instabilities. In the first type, plumes rise from the lower mantle, and corresponding unstable regions of lithosphere drip back into the mantle.
The silicate mantle of the Earth's moon is approximately 1300–1400 km thick, and is the source of mare basalts. [4] The lunar mantle might be exposed in the South Pole-Aitken basin or the Crisium basin. [4] The lunar mantle contains a seismic discontinuity at ~500 kilometers (310 miles) depth, most likely related to a change in composition. [4]
Atmospheric circulation is the large-scale movement of air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth. The Earth's atmospheric circulation varies from year to year, but the large-scale structure of its circulation remains fairly constant.
The influence of the evolution of life has to be taken into account rather soon in the history of the atmosphere because hints of earliest life forms appeared as early as 3.5 billion years ago. [48] How Earth at that time maintained a climate warm enough for liquid water and life, if the early Sun put out 30% lower solar radiance than today, is ...
The pressure at the bottom of the mantle is ≈140 GPa (1.4 Matm). [24] The mantle is composed of silicate rocks richer in iron and magnesium than the overlying crust. [25] Although solid, the mantle's extremely hot silicate material can flow over very long timescales. [26] Convection of the mantle propels the motion of the tectonic plates in the
Simulation of thermal convection in the Earth's mantle. Hot areas are shown in red, cold areas are shown in blue. A hot, less-dense material at the bottom moves upwards, and likewise, cold material from the top moves downwards. Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid.